A cost of viviparity and parental care in scorpions : reduced sprint speed and behavioural compensation

Abstract Current reproductive effort may often be at the expense of future reproduction. One way in which future reproduction of viviparous animals may be affected is by increased risk of predation resulting from decreased mobility associated with pregnancy. The common striped scorpion, Centruroides vittatus , may experience considerable risk of predation associated with reproduction because it is viviparous, with an eight-month gestation period. C. vittatus also carries the newborn young on its back during their first instar. The purpose of this study was to establish a cost of viviparity and parental care in these scorpions by determining sprint speed at three reproductive stages: pregnant, carrying offspring and post-dispersal of offspring. Post-dispersal speed was used as a best estimate of non-pregnant speed. Pregnant speeds averaged 84% of post-dispersal speeds. Lower speeds were correlated with absolute and relative measures of litter size. Speed while carrying offspring averaged 61% of post-dispersal speed, and was correlated with mass of the litter and number of individuals in the litter. Sixty-five per cent of the females carrying young could not be induced to run; these females instead assumed a defensive posture. Results indicate that female scorpions experience a cost (in decreased running speed) to viviparity and parental care, and that some females may reduce this cost by using an alternative defensive strategy.